Terminally differentiated urothelial cells accumulate a tremendous number of cytoplasmic vesicles composed of the so-called asymmetric unit membrane (AUM; also known as t79thelial. plaques). These vesicles, by fusion with the apical surface, are the source of the rigid-looking urothelial plaques (0.2 -0.5 um diameter that cover over 70% of the urothelial apical surface. By this fusion and their possible retrieval as vesicles back into the cytoplasm, these plaques are thought to play a role in regulating (reversibly) the apical surface are during the micruation cycle. The association of the membranes with an underlying cytoskeleton may anchor the apical plaques thus preventing the apical surface from rupturing during bladder distention. The purpose of this project is to'better understand how the urothelial plaques, including those in the vesicles and those on the apical surface, interact with the cytoskeleton; and how this interaction may vary during bladder distention and contraction. With this as a baseline, we will later study how such interactions may be altered in mice that are deficient (via gene targeting) in some of the uroplakins, the major protein subunits of AUM. We will use the de-embedding procedure developed by Hans Ris to study sections through the apical surface in the high resolution SEM. In addition, thick sections will be examined in the energy filtered TEM in order to visualize the dime-dimensional organization of the cytoskeleton of urothelial cells.